First, to call it timing on a diesel is actually an incorrect term. What it is really called is Start of Injection, or SOI. For the remainder, I will use this term when referring to diesels.

In essence, the two terms (timing and SOI) are fairly interchangeable as they both relate to some point in the crankshaft rotation where combustion occurs. The difference is that on a gasoline engine, the point of combustion is fairly exact (the point where the spark plug fires) while on the diesel engine, the point of combustion varies depending on cylinder temperature, cylinder pressure, air temperature, fuel temperature, fuel pressure (as it is injected), and when the injection event occurs (SOI). Some parameters have more of an influence that others, but for the sake of comparison we'll say that the point of injection is more or less the point of combustion.

Like any other combustion engine, the point of combustion must be timed in order to achieve a flame front that smoothly heats the air and provides useful, downward pressure on the piston. If the combustion occurs too late, the energy is wasted "chasing" the piston down the stroke. If the combustion occurs too early, the energy "stalls" the piston on the upward stroke, creating immense stress on the piston, rod, crankshaft and block. To paint this a little more figuratively, you can think of excessive timing as a sort of thermal hydrolock, and the affects are actually quite similar.

I think it's safe to say that Ford's tuning is a bit conservative so when we look at the stock SOI curve with 24º at 3500 RPM, I think that the stock curve would be a good place to use for comparison against what would be considered ideal, aggressive or excessive.

Any internal combustion engine is going to suffer engine failure if the flame front occurs to soon. It doesn't matter if it's a piston engine or a rotary engine, gas engine or diesel. By causing the combustion process too early, the piston becomes a stop-block and all the reciprocating or rotating components are "shocked" into deceleration and load bearing structures (especially the connecting rod) are stressed to the point where they eventually fail.

The only real analogy I can offer is to think of a bicycle where the chain is directly attached to the wheel (no free-wheel). As you pedal, you are pushing down on the crank after the crank has reached the top, in most cases about 30º after reaching the top. If you push exactly as the crank reaches the top, you're expending energy but it's not really accomplishing anything as the crank is not at an angle to utilize the energy being expended. At some point your leg would become fatigued but no real damage. Now, if you push the crank as it is traveling upwards, the result depends on the energy being expended (how hard you're pushing). Push down a little and all you do is slow down. Push down hard or lock your leg, and you're going over the handlebars. If your leg was strong enough, you'd snap the crank. I know it's a silly analogy, but it really is a good comparison.

As I said, the Ford tuning is a bit conservative. We've seen performance gains as well as efficiency gains with moderate timing and fuel increases. However, you can't dispute the general dynamics of the internal combustion engine. The fact is that timing / SOI / combustion that is too advanced can, and will, destroy an engine. Just ask any Gen 2 Lightning owner what happens with only 2º or 3º too much advance. They have PMRs too and you only need detonation 1 time to window the block.

I hope this helps.